Some ideas that come to mind:
- the standby server cannot garantee 100% no data loss even with
Dataguard because the primary host can go down before the Dataguard
copies the changes to the standby.
- there are other options except for standby server. For example, the
VCS cluster has better chances to provide 100% no data loss because
even if the host does go down, the filesystems can be mounted from
another box and Oracle can do instance recovery.
- you will have to do a lot of automation work if you are not using
Dataguard. First of all, the managed recovery switches off if it
encounters any problems, e.g. a network failure. It does not switch
back on, and archived log files generated during the period it was
off need to be manually transfered to standby and applied. You will
need a mechanism to watch it and transfer files. What you might find
yourself doing is to ignore the managed recovery and write your own
scripts to transfer files. On that route, you will encounter a lot of
obstacles if you try to make it close to what Dataguard does.
- the DataGuard (and 9iR2) software is relatively new and is probably
full of bugs. If your system is critical, you may consider not to test
out
the Oracle bugs on it. 8i software has plenty bugs as well but they are
KNOWN :).
- when planning for failover implementation, you need to know your
requirements. There are other things to consider except for data loss.
For example, how quickly the system needs to become available. You
also need to define the types of disaster you are trying to protect your
system from. And to get an idea what it's going to cost you (your
company).
I have seen several posts mentioning the performance impact by
DataGuard. I am pretty sure there's got to be some, but maybe somebody
could elaborate on this and let me know what this performance impact
is due to?
Another question I am trying to get answered: how does DG manage
TWO standby databases? What happens with redo data if one of them
is temporarily unavailable?
Thank you for any answers.
Regs
AK
Chris Forbis wrote:
> I am looking into ways of recovering in the case of a major failer on
> a primary server. I have the idea to create a standby server, and
> this seems to take care of much of the work. The problem I see is
> when the primary system fails, and a log switch has not happened in
> the last 4 minutes, It seems I loss that 4 minutes of data because the
> log has not been archived and moved.
>
> Ideas of how to get 100% no data loss?
>
> Thanks
>
> Chris
Received on Wed Oct 16 2002 - 16:18:19 CDT
